Method of producing phosphoric acid and hydrogen



' Patented Mar. 24, 1931 at a high temperature.

UNITED STATES PATENT OFFICE MARKUS LARSSON, 0F BERLIN, GERMANY,ASSIGNOR, BY MESNE ASSIGNMENTS, TO DU PONT AMMONIA CORPORATION, OFWILMINGTON, DELAWARE, A CORPORATION 01' DELAWARE METHOD OF PRODUCINGPHOSPHORIC ACID AND HYDROGEN Original application filed March 31, 1925,Serial No. 19,581. Divided and. this application filed January 26, 1929.Serial No. 335,283. 7 V

This invention relates to the production of phosphoric acid andhydrogen, the present application being a division of my co-pendingapplication Serial No. 19,581, filed March- 31, 1925. 1

It has already been proposed to produce phosphoric acid throughreduction of water y means of elementary phosphorus at a hightemperature so that the phosphorus is oxidized to phosphoric acid by theoxygen ofthe water, setting the hydrogen free. After the hydrogen hasbeen separated from the phosphoric acid it is obtained in a practicallypure form. In order to facilitate the reaction between water andphosphorus so that it can take place at alower temperature and withgreater velocity than otherwise and avoiding the formation of phosphine,it has been proposed touse certain metals or their oxides as catalyzers.Generally this reaction is carried out by the useof gaseous phosphorus,which is obtained by reducing phosphatic material bycarbon in anelectric reduction furnace. The aim of the present invention is also toproduce but in a different way phosphoric acid fromphosphorus andwaterobtaining at the same time free hydrogen as a by-product. The presentinvention consists chiefly in that a phosphide of a metal reducible byhydrogen is brought to react with water or watervapor The metallicphosphide can be produced by reducing phosphatic material by carbon inan electric or other suitable reduction furnace adding the metal oroxides of same so that the metallic phosphide is obtained as a moltenfluid (Fe P melts at 1290 C.) which is tapped off from the furnace andthen brought to react with superheated steam, for example, in aBesseiner converter; or the phosphide can also be 7 V sorbed during theformation of metallic phosphide, which afterwards is reacted upon bymeans of superheated steam. During the reaction between the metallicphosphide and the steam, the phosphorus of the phosphide is oxidized bymeans of the oxygen of the steam principally to phosphorus pentoxide atthe same time setting hydrogen free. The metal combined with thephosphorus is also set free or changed into oxide, while at the sametime a corresponding quantity of'hydrogen gas is set free. ,The metaloroxide can again be used either as an addition in the reduction furnaceor for absorption of a new quantity of phosphorus, in which latter casethe metal first must be reducedfif it was changed into oxide at thetreatment of the phosphide with steam. In that way the process can becarried on without any essential loss of metal.

It is not necessary for the conversiono'f metallic phosphide intophosphorus pentoxide to use exclusively the oxygen of the water. Theinvention also covers the case in whichpart of the oxygen required isadded in the form of free oxygen. In this case steam and air may eitherbe mixed in advance in the desired proportions, before being broughttogether with the metallic phosphide, or else water or steam may beadded and then air or vice versa. tion may be used either when it isdesired to obtain hydrogen gas mixed with a certain percentage ofnitrogen, or when required for same, etc.

The metals that, may be used in the present invention are the metals ofthe eighth group of the periodic system Fe, Ni, Co, Ru, Rh, Pd, Os, Irand Pt, of the seventh group This modification of the inven- Mn, of thesixth group Cr, Mo, W and U,

and of the first group Cu," Ag and Au. Several of these are, however,mainly of theoretical interest. v

In Figs. 1-3 ofthe attacheddrawing a schematic view is shown of theapparatus for performing three different ways of carrying out theinvention. a v In Fig. 1, A indicates an electric reduction furnacewhich is chargedwith phosphate rock, carbon, silica and a metal, or ametal oxide, which is reducible by means of hydrogen,

for instance, copper in metallic form or an oxidized copper ore. Thephosphorous produced from the phosphate rock combines with the metalpresent into metallic phosphide, which gathers in melted format thebottom of the furnace under the melted slag formed simultaneously, whichslag consists mainly of calcium silicate. The furnace A is provided withelectrodes B, slag removing holes C, gas outlet D and a tube E throughwhich the phosphide produced in the furnace may be drawn offperiodically into a Bessemer converter F. After the converter has beenfilled to the required height with melted metallic phosphide, steam orsteam mixed with a small quantity of air is blown into same through atube, G whereby the phosphorous in the metallic phesphide is oxidizedinto phosphorous pent'oxide, which volatilizes at the same time as themetal is reduced and the'steam decomposed, so that free hydrogen isobtained. The temperature in the con verter should be kept so high thatthe reduced metal will beikept in a liquid condition and so that, at theend of the reaction, it can be drawn off through the tube N. Thisregulation of the temperature can be accomplished by regulating thetemperature of the steam and also by regulating the quantity of airadded. The phosphorous pentoxide and with phosphate rock, silica andcarbon without the addition of any metal or metallic oxide, so thatthere only takes place a reduction of the phosphate rock which producesa gaseous mixture of elementary phosphorus and carbon monoxide, whichmixture is passed through a tube'D into a chamber F filled with piecesof a metal, for instance, copper which is kept at a temperatureexceeding 400 centrigrade. In this chamber the phosphorous is absorbedby the metal forming a metallic'phosphide, while the remaining carbonmonoxide escapes through a tube M and 1 is then used for the productionof steam, for

heating the charge, etc. When the copper in the chamber F has absorbedthe proper quantity of phosphorous, the flow of gas is changed from thefurnace to another absorption chamber F and properly superheated watervapor is brought into the chamber F through the tube 'Gr. In this waythe metallic phosphide is reduced to metal at the same time as the watervapor is decomposed. The

gaseous reaction products formed consisting of phosphorous pentoxide andhydrogen gas are conducted through the tube H into the cooler or boilerK and the separation system L Where the phosphorus pentoxide iscondensed and separated .in the well lmown way. By utilizing alternatelyin the'manner d'e scribed both of the chambers .F and F2 for theabsorption of the phosphorus'by means of a metal insolid form and-thereduction of the metallic phosphide by means of water vapor, the processmay .be carried on continuously.

In the method shown in Fig. 3 the electric furnace A is used as shown inFig. 2 for the reduction of phosphatic rock and the absorp tion of thegaseous phosphorus coming from the reduction furnace takes place in achamber F containing melted metal, such as for instance, melted copper.Through a partition O,part of which depends from the roof of the chamberinto the melted metal, the gas room of the chamber is divided in twoparts,

9 and 92, which are not connected with each other. A fan or some othersuitable-device disposed in the conduit D serves to force the gasescoming from the furnace A in a.

finely divided form under the surface of the metal in the part 9 inorder that an efieetive absorption shall take place. The carbon monoxideleaves part 9 through the tube M and is utilized in a suitable way. Whenthe gases pass the molten metal bath they produce a movement in same sothat the phosphide formed is partly transferred to the other part of thechamber (9 Into this superheated steam is blown through the tube G bywhich the metallic phosphide is re- W ducedto metal, which throughcirculation is carried back to part 9 where it absorbs new quantities ofphosphorus while the separated phosphorus pentoxide together with the bydro'gen free by the reduction are brought through the conduit H to thecooler or boiler" K and to the separating system L where, the phosphorus'pentoxide is separated in the usual way. i i

' ioo When the metallic phosphide is produced directly in thereductionfurnace .it is of' course not necessary to treat it by means of steamimmediately after it has been drawn off from the reduction furnace. Itsometimes by means of steam. When the metallic phosphide is producedoutside the reduction furnace by reacting upon a metal by means of thegas coming from a furnace for the reduction of phosphate rock thehydrogen 7 may be of advantage to first let it cool off and f solidify,granulate it and afterwards treat it acting upon phosphide of iron bymeans of hydrogen monoxide at an elevated temperature to oxidize thephosphorus of the phosphide substantially into phosphorus pentoxide andto set free the hydrogen of the hydrogen monoxide.

2. The invention set forth in claim 1 in which free oxygen is added tothe hydrogen monoxide.

In testimony whereof, I aflix my signature.

, MARKUS LARSSON.

